This is an
excellent question, but to me, I felt like this strip was more open-ended in
how you interpreted it. That’s why I didn’t include France, as it wasn’t solidly
confirming anything.

Here’s the
full justification for it.

England’s
sleeping, surrounded by his fairie friends. Like you said, they get scared when
they hear France knocking on the door.

Judging by
France’s reaction here, this is the first time he’s seeing fairies.

Then, you
have England’s flustered reaction about France not knocking.

Taken together,
it seems like England letting his guard down by sleeping might have actually
activated his powers in allowing France to see the fairies. We’re only given
information about the fact that he has this ability when nations come to his house, not whether he can consciously
or unconsciously evoke and control it.

Of course,
with Hetalia, the one exception to the rule always seems to be Halloween. The
fairies/ ghosts have no problem showing themselves to skeptics then. 

Ex: France
encounters Napoleon’s ghost during the 2013-2014 Christmas Event.